Aggregate of semiconductor micro-needles and method of manufacturing the same, and semiconductor apparatus and method of manufacturing the same

ABSTRACT

On a silicon substrate is formed a silicon dioxide film and then hemispherical grains made of silicon, each having an extremely small diameter, are deposited thereon by LPCVD. After annealing the hemispherical grains, the silicon dioxide film is etched using the hemispherical grains as a first dotted mask, thereby forming a second dotted mask composed of the silicon dioxide film. The resulting second dotted mask is used to etch the silicon substrate to a specified depth from the surface thereof, thereby forming an aggregate of semiconductor micro-needles. Since the diameter of each of the semiconductor micro-needles is sufficiently small to cause the quantum size effects as well as has only small size variations, remarkable quantum size effects can be obtained. Therefore, it becomes possible to constitute a semiconductor apparatus with a high information-processing function by using the aggregate of semiconductor micro-needles (quantized region).

This application is a Divisional of Application Serial No. 08/333,320filed Nov. 2, 1994, now U.S. Pat. No. 6,033,928.

BACKGROUND OF THE INVENTION

In recent years, there has been developed an optical element in whichporous silicon is formed to be used as a light emitting element.Japanese Laid-Open Patent Publication No. 4-356977 discloses such anoptical element, in which a large number of micro-pores 102 are formedin the surface region of a silicon substrate 101 by anodization, asshown in FIG. 33. If the porous silicon is irradiated with light,photo-luminescence having its absorption edge in the visible region isobserved, which implements a light-receiving/light-emitting elementusing silicon. That is, in a normal semiconductor apparatus composed ofsingle-crystal silicon, an excited electron makes an indirect transitionto a lower energy level so that the energy resulting from the transitionis converted into heat, which renders light emission in the visibleregion difficult. However, there has been reported a phenomenon that, ifsilicon has a walled structure, such as porous silicon, and its wallthickness is about 0.01 μm, the band width of the silicon is enlarged to1.2 to 2.5 eV due to the quantum size effects, so that an excitedelectron makes a direct transition between the bands, which enableslight emission.

It has also been reported that two electrodes are provided on both endsof the porous silicon so that electroluminescence is observed by theapplication of an electric field.

However, if electroluminescence is to be obtained by the application ofan electric field or photoluminescence is to be obtained by theirradiation with light of the porous silicon formed by anodization inthe surface region of the silicon substrate 101 as shown in FIG. 33, thefollowing problems are encountered.

That is, the diameter and depth of the micro-pore 102 formed byanodization are difficult to control. In addition, the configuration ofthe micro-pore 102 is complicated and the distribution of its wallthickness is extremely random. As a result, if etching is intenselyperformed in order to reduce the wall thickness, the wall portions maybe partially torn and peeled off the substrate. Moreover, since thedistribution of the wall thickness is random, the quantum size effectsare not generated uniformly over the whole wall portions, so that lightemission with a sharp emission spectrum cannot be obtained. Furthermore,the wall surface of the micro-pore in the porous silicon readily adsorbsmolecules and atoms during anodization, due to its complicatedconfiguration. Under the influence of the atoms and molecules attachedto the surface of the silicon, the resulting optical element lacks thecapability of reproducing a required emission wavelength and itslifespan is also reduced.

On the other hand, with the development of the presentinformation-oriented society, a semiconductor apparatus in which asemiconductor integrated circuit is disposed has presented an increasingtendency toward the personalization of advanced info-communicationappliances with large capacities. In other words, there has been ademand for appliances which enable advanced information transmission toand from a hand-held computer or cellular phone. To meet the demand, itis required to not only enhance the performance of the conventionalsemiconductor apparatus, which processes only electric signals, but alsoimplement a multi-function semiconductor apparatus which processeslight, sounds, etc., as well as electric signals. FIG. 34 shows thecross sectional structure of a three-dimensional integrated circuitsystem that has been developed in order to satisfy the requirements.Such a three-dimensional integrated circuit system is expected tosurmount the miniaturization limit inherent in the conventionaltwo-dimensional integrated circuit system as well as improve anddiversify functions to be performed. In the drawing, a PMOSFET 110 aconsisting of a source 103, a drain 104, a gate oxide film 105, and agate 106 is formed in the surface region of an n-well 102, which isformed in a p-type silicon substrate 101 a as a first layer. In thesurface region of the first-layer silicon substrate 110 a are formedsemiconductor apparatus including an NMOSFET 110 b consisting of thesource 103, drain 104, gate oxide film 105, and gate 106. There are alsoformed a connecting wire 107 between the source and drain regions and aninter-layer insulating film 108 for covering each region, which has beenflattened. On the inter-layer insulating film 108 is formed asecond-layer silicon substrate 101 b made of single-crystal silicon. Onthe second-layer silicon substrate 101 b are also formed semiconductorapparatus such as the PMOSFET 110 a and NMOSFET 110 b, similarly to thesemiconductor apparatus on the above first-layer silicon substrate 101a. The semiconductor apparatus in the first layer and the semiconductorapparatus in the second layer are electrically connected via a metalwire 109 (see, e.g., “Extended Abstracts of 1st Symposium on FutureElectron Devices,” p. 76, May 1982).

However, such a three-dimensional integrated circuit system has thefollowing problems. The wire 109 is formed by a deposition method inwhich, after a contact hole was formed, a wiring material is depositedand buried in the contact hole. Since the resulting contact hole becomesextremely deep, deficiencies such as an increase in resistance value anda break in wiring are easily caused by a faulty burying of the wiringmaterial, resulting in poor reliability. With such problematicmanufacturing technology, it is difficult to implement athree-dimensional integrated circuit system which can be usedpractically. In particular, it is extremely difficult to implement anintegrated circuit system in more than three dimensions.

SUMMARY OF THE INVENTION

The present invention has been achieved by focusing on the fact that, ifa structure in which a large number of semiconductor micro-needles arearranged is used instead of a porous structure, the diameters of thesemiconductor micro-needles become uniform. It is therefore a firstobject of the present invention to provide a quantized region forimplementing intense light emission with a narrow wavelengthdistribution, such as electroluminescence or photoluminescence, andconversion of optical signals to electric signals.

A second object of the present invention is to provide a semiconductorapparatus with an advanced information processing function byincorporating an aggregate of semiconductor micro-needles with varioussignal converting functions into an integrated circuit system.

To attain the above first object, an aggregate of semiconductormicro-needles according to the present invention comprises, as theirbasic structure, a large number of semiconductor micro-needlesjuxtaposed in a substrate, each of said semiconductor micro-needleshaving a diameter sufficiently small to cause the quantum size effects.

With the basic structure, the band width of a semiconductor materialcomposing the semiconductor micro-needles is expanded due to theso-called quantum size effects. As a result, the direct transitions ofelectrons occur even in a semiconductor material such as silicon inwhich excited electrons make indirect transitions in the proper size tocause the quantum size effects. Consequently, it becomes possible toconstitute a light emitting element, wavelength converting element,light receiving element, or the like in which the aggregate ofsemiconductor micro-needles is disposed by using the photoluminescenceand electroluminescence resulting from the quantum size effects of eachsemiconductor micro-needle, variations in electric characteristicscaused by the radiation of light, and the like. In this case, unlike aconventional quantized region composed of silicon with a porousstructure or the like, the quantized region according to the presentinvention is constituted by the aggregate of semiconductormicro-needles, so that the diameter of each semiconductor micro-needlebecomes sufficiently small to cause significant quantum size effects andbecomes uniform even if the diameter faces any direction in a planeperpendicular to the axial direction.

In the structure of the above aggregate of semiconductor micro-needles,it is preferable that each of the above semiconductor micro-needles isformed substantially perpendicular to the surface of the above substrateand that the above semiconductor micro-needles are formed discretely.

In the above aggregate of semiconductor micro-needles, a protectivelayer can be obtained by forming an insulating layer on the sideportions of the semiconductor micro-needles. In particular, it becomespossible to obtain light from the lateral side of the semiconductormicro-needles by composing the insulating layer of an oxide.

By composing the insulating layer of two layers of an inner oxide layerand an outer nitride layer over the inner oxide layer, it becomespossible to exert a compressive stress on each semiconductormicro-needle without preventing the obtention of light from the lateralside of the aggregate of semiconductor micro-needles, thereby remarkablyexerting the quantum size effects.

To attain the above second object, a semiconductor apparatus accordingto the present invention comprises as its basic structure: a siliconsubstrate; and a quantized region composed of an aggregate ofsemiconductor micro-needles, each of said semiconductor micro-needlesextending from the surface of the above silicon substrate to a specifieddepth and having a diameter sufficiently small to cause the quantum sizeeffects.

With the basic structure, there can be implemented a semiconductorapparatus with excellent performance utilizing the remarkable quantumsize effects of the aggregate of semiconductor micro-needles describedabove. Hereinafter, it will be assumed that an electric signal andoptical signal input to the quantized region are a first electric signaland first optical signal, respectively, while signals output from thequantized region are a second electric signal and second optical signal,respectively.

The following elements can be added to the basic structure of the abovesemiconductor apparatus.

It is possible to provide an optical-signal generating means forgenerating a first optical signal so that the first optical signal ismade incident upon the above quantized region and that the above firstquantized region receives the first optical signal from the aboveoptical-signal generating means and generates a second optical signal.With the structure, the quantized region functions as an opticalconverting element.

It is possible to form a trench in a part of the above silicon substrateand to provide the above quantized region and optical-signal generatingmeans on both sides of the above trench, so that they face each other.With the structure, the semiconductor apparatus constitutes atwo-dimensional integrated circuit system with an advanced informationprocessing function comparable to a three-dimensional integrated circuitsystem.

It is possible to provide an upper electrode over the above quantizedregion so that the upper electrode is electrically connected to theupper end of each of the above semiconductor micro-needles. With thestructure, it becomes possible to convert electric signals into opticalsignals and vice versa via the quantized region.

It is possible to add optical detecting means for receiving the secondoptical signal generated in the above quantized region and generating athird electric signal.

It is possible to provide the above light detecting means in a portiondifferent from the above quantized region of the above silicon substrateand to compose the above light detecting means of an aggregate ofsemiconductor micro-needles each having a diameter sufficiently small tocause the quantum size effects.

It is possible to constitute the quantized region of the above basicstructure so that it receives a first optical signal and generates asecond electric signal and it is possible to provide: optical-signalgenerating means for generating the above first optical signal so thatthe first optical signal is made incident upon the above quantizedregion; and an electric circuit for processing the second electricsignal generated in the above quantized region.

It is possible to provide stress generating means for generating astress in each of the above semiconductor micro-needles in the abovequantized region, the above stress being in the axial direction of eachof the above semiconductor micro-needle, and to constitute the abovequantized region so that it receives the above first electric signal andgenerates the second optical signal having a wavelength corresponding tothe stress in each of the above semiconductor micro-needles. With theabove structure, the semiconductor apparatus is provided with aforce-to-optical signal converting function. In this case, theforce-to-optical signal converting function is particularly enhanced bycomposing the above stress generating means of the above upper electrodeand of a probe connected to the upper electrode so as to transmit amechanical force from the outside.

The upper electrode of the above basic structure can be made of atransparent material. With the structure, it becomes possible to inputthe first electric signal to the quantized region without preventing theobtention of the second optical signal from each semiconductormicro-needle in the quantized region in its axial direction.

It is possible to provide on the above upper electrode a condensingmeans, such as a concave lens, for condensing the second optical signalgenerated in the above quantized region, which functions as alight-emitting element for generating the second optical signal. It isalso possible to divide the above quantized region into a plurality oflinearly striped quantized regions in which the aggregate of the abovesemiconductor micro-needles is formed into linear stripes in a planeparallel to the surface of the silicon substrate, to provide linearlystriped discrete layers for separating and insulating the above linearlystriped quantized regions so that each linearly striped discrete layeris interposed between any two adjacent linearly striped quantizedregions, and to alternately arrange the above linearly striped quantizedregions and linearly striped discrete layers so as to constitute aone-dimensional Fresnel lens. It is also possible to divide the abovequantized region into a plurality of ring-shaped quantized regions inwhich the aggregate of the above semiconductor micro-needles is formedinto rings in a plane parallel to the surface of the silicon substrate,to provide ring-shaped discrete layers for separating and insulating theabove ring-shaped quantized regions so that each ring-shaped discretelayer is interposed between any two adjacent ring-shaped quantizedregions, and to alternately arrange the above ring-shaped quantizedregions and ring-shaped discrete layers so as to constitute a two-dimensional Fresnel lens.

It is also possible to arrange a plurality of the above quantizedregions so as to form a specified flat pattern in the above siliconsubstrate, thereby constituting the semiconductor apparatus so that itfunctions as an optical display device.

It is possible to dispose an LSI provided with an additionalself-checking circuit on the above silicon substrate and to provide theabove quantized region in the self-checking circuit of the above LSI.

Next, to attain the above first object, a method of manufacturing theaggregate of semiconductor micro-needles according to the presentinvention comprises the steps of: forming on a silicon substrate adotted mask for covering a large number of dot regions each having adiameter sufficiently small to cause the quantum size effects of theabove semiconductor; and etching the above silicon substrate by usingthe above dotted mask so as to form a large number of semiconductormicro-needles each extending from the surface of the above siliconsubstrate to a specified depth.

In accordance with the method, there can be formed the aggregate ofsemiconductor micro-needles which exerts remarkable quantum sizeeffects.

In the step of forming the above dotted mask, it is possible to deposita large number of granular materials, each having a diametersufficiently small to cause the quantum size effects of the abovesemiconductor, directly on the above silicon substrate so that thegranular materials constitute the dotted mask. In accordance with themethod, the aggregate of semiconductor micro-needles, which is differentin structure from the conventional porous semiconductor, can be formedeasily. It is also possible, in the step of forming the above dottedmask, to form a photoresist film on the above silicon substrate and thenmechanically remove a part of the above photoresist film by means of aprobe needle of a cantilever of an atomic force microscope so that thedot regions remain and that the remaining portions of the photoresistfilm constitute the above dotted mask. It is also possible to apply aphotoresist onto the above silicon substrate and then pattern the abovephotoresist film so that dot-matrix-pattern portions resulting from theinterference of light remain and that the above remaining portions ofthe photoresist film constitute the above dotted mask.

In the step of forming the above dotted mask, it is possible to form aninsulating film on the above silicon substrate and to further form apre-dotted mask for covering a large number of minute dot regions on theabove insulating film so that the above insulating film is patternedusing the pre-dotted mask and that the remaining portions of theinsulating film constitute the above dotted mask.

As the above granular materials, it is possible to use grains of asemiconductor material, metal seeds serving as nuclei for the growth ofthe grains of a semiconductor material, a <311>-oriented siliconcrystal, amorphous silicon, or the like.

After the formation of the above granular materials, it is possible toperform the step of annealing the above granular materials at least onceso as to reduce the interface after the formation of the above granularmaterials. With the annealing step, each of the resulting granularmaterials presents an excellent configuration closer to a sphere.

Furthermore, in forming the above quantized region, it is also possibleto perform the step of forming an insulating layer so as to surroundeach of the above semiconductor micro-needles. In accordance with themethod, it is possible to prevent an impurity from entering into eachsemiconductor micro-needle as well as discharge the impurity out of thesemiconductor micro-needle.

The step of forming the above insulating layer is preferably performedby filling up the space surrounding each of the above semiconductormicro-needles with the insulating layer. The step of forming the aboveinsulating film can also be performed by CVD or by thermally oxidizingthe surfaces of the semiconductor micro-needles.

To attain the above second object, a method of manufacturing thesemiconductor apparatus according to the present invention comprises thesteps of: forming on a silicon substrate a dotted mask for covering alarge number of dot regions each having a diameter sufficiently small tocause the quantum size effects of the above semiconductor; etching theabove silicon substrate by using the above dotted mask so as to form alarge number of semiconductor micro-needles each extending from thesurface of the above silicon substrate to a specified depth; removingthe above dotted mask; and forming an upper electrode electricallyconnected to each semiconductor micro-needle over the upper ends of theabove semiconductor micro-needles.

In accordance with the method, a semiconductor apparatus with theadvanced information processing function as described above can easilybe manufactured.

It is possible to further provide the step of forming a p-n junction inthe above silicon substrate and form, in the above step of forming anaggregate of semiconductor micro-needles, the semiconductormicro-needles by performing etching to a point at least lower than theabove p-n junction. In accordance with the method, a p-n junction isformed in each semiconductor micro-needle, thereby enhancing the quantumsize effects.

It is also possible to perform the step of forming a discrete insulatinglayer which surrounds the above aggregate of semiconductor micro-needlesso that the aggregate of semiconductor micro-needles is laterallyisolated from other regions. In this case, it is preferable to furtherperform the step of forming at least one lateral electrode to beconnected to the silicon substrate through the above discrete insulatinglayer. In accordance with the method, it becomes possible to input andobtain an electric signal from the lateral side of the quantized region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a semiconductor apparatus accordingto a first embodiment;

FIGS. 2(a) to 2(e) are cross sectional views showing the transition ofthe structure of the semiconductor apparatus according to the firstembodiment during its manufacturing process;

FIG. 3 is a view showing variations in the configuration of ahemispherical grain when the deposition temperature and the partialpressure of SiH₄ are varied in the first embodiment;

FIGS. 4(a) to 4(c) are transverse sectional views showing the structureof an aggregate of semiconductor micro-needles formed using grains inthe amorphous region by a manufacturing method of the first embodiment,the structure of an aggregate of semiconductor micro-needles formedusing grains in the <311>-oriented region by the manufacturing method ofthe first embodiment, and the structure of conventional porous siliconformed by anodization, respectively;

FIG. 5 is a view showing the characteristics of current with respect tovoltage applied to a quantized region;

FIG. 6 is a view showing the dependence of light emission intensity oncurrent in the quantized region;

FIG. 7 is a view showing the dependence of emission wavelength onvoltage in the quantized region;

FIGS. 8(a) to 8(e) are cross sectional views showing the transition ofthe structure of the semiconductor apparatus according to a secondembodiment during its manufacturing process;

FIG. 9 is a view showing variations in the configuration of thehemispherical grain when the deposition temperature and the partialpressure of SiH₄ are varied in the second embodiment;

FIGS. 10(a) to 10(c) are SEM photographs showing variations in theconfigurations of the hemispherical grains when annealing conditions arevaried;

FIG. 11 is a view showing the relationship between the annealing periodand the grain diameter and density of the hemispherical grains in athird embodiment;

FIGS. 12(a) and 12(b) are cross sectional views showing the transitionof the grains according to a fourth embodiment during their formationprocess;

FIG. 13 is a view showing a difference in the grain distribution andgrain diameter between the case where a surface treatment was performedand the case where the surface treatment was not performed in the fourthembodiment;

FIG. 14 is a cross sectional view of a semiconductor apparatus accordingto a fifth embodiment;

FIG. 15 is a cross sectional view of a semiconductor apparatus accordingto a sixth embodiment;

FIG. 16 is a cross sectional view of a semiconductor apparatus accordingto a seventh embodiment;

FIGS. 17(a) and 17(b) are views diagrammatically showing the planestructure of a one-dimensional Fresnel lens and the plane structure of atwo-dimensional Fresnel lens;

FIG. 18 is a cross sectional view of a semiconductor apparatus accordingto an eighth embodiment;

FIG. 19 is a view for illustrating the movement of electrons in acrystal lattice of silicon to which radio-frequency electric power hasbeen applied;

FIG. 20 is a cross sectional view of a semiconductor apparatus accordingto a ninth embodiment;

FIGS. 21(a) to 21(c) are cross sectional view showing the transition ofthe structure of the semiconductor apparatus according to the ninthembodiment during its manufacturing process;

FIG. 22(a) to 22(d) are cross sectional views for illustrating theprinciple of a stress sensor utilizing the quantized region according toa tenth embodiment;

FIGS. 23(a) and 23(b) are views showing the cross sectional structure ofthe stress sensor of the tenth embodiment and variations in thewavelength of output light from the stress sensor with respect tovariations in stress, respectively;

FIG. 24 is a block diagram showing the overall structure of thesemiconductor apparatus according to the tenth embodiment;

FIGS. 25(a-1) to 25(d-2) are cross sectional views and plan viewsshowing the transition of the structure of the semiconductor apparatusaccording to an eleventh embodiment during its manufacturing process;

FIG. 26 is a plan view of a display apparatus according to the eleventhembodiment;

FIG. 27 is a cross sectional view partially showing a first lightemitting unit of the semiconductor apparatus according to the eleventhembodiment;

FIGS. 28(a) and 28(b) are cross sectional views and plan views showingthe structure of a sound-wave sensor unit in the semiconductor apparatusaccording to the eleventh embodiment;

FIG. 29 is a cross sectional view showing the structure of thesound-wave output unit in the semiconductor apparatus according to theeleventh embodiment;

FIGS. 30(a) to 30(d) are cross sectional views showing the transition ofthe structure of the semiconductor apparatus according to a twelfthembodiment during its manufacturing process;

FIG. 31 is a cross sectional view of the semiconductor apparatusaccording to the twelfth embodiment;

FIGS. 32(a) to 32(d) are cross sectional views showing the transition ofthe structure of the semiconductor apparatus according to a thirteenthembodiment during its manufacturing process;

FIG. 33 is a cross sectional view of the conventional porous siliconformed by anodization; and

FIG. 34 is a cross sectional view partially showing a conventionalthree-dimensional integrated circuit system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the embodiments of the present invention will be described withreference to the drawings.

(First Embodiment)

A description will be given first to a first embodiment. FIG. 1 is across-sectional view of an optical semiconductor apparatus according tothe first embodiment. As shown in the drawing, the semiconductorapparatus comprises: a silicon substrate 1 of single-crystal structure;a large number of semiconductor micro-needles 2 extending from thesurface of the silicon substrate 1 to a specified depth so that theaxial direction thereof is perpendicular to the surface of the substrate1; an insulating layer 3 composed of a silicon dioxide film which fillsup the space surrounding each semiconductor micro-needle 2; and atransparent electrode 4 formed on the flattened top ends of thesemiconductor micro-needles 2 and the insulating layer 3. An aggregateof the foregoing semiconductor micro-needles 2 functions as a quantizedregion Rqa. Those ends of the above semiconductor micro-needles 2 whichare closer to the substrate 1, hereinafter referred to as “base ends,”are held in combination by the substrate 1. Each semiconductormicro-needle 2 has a diameter of about 2 to 50 nm. The above insulatinglayer 3 is formed by subjecting the surface region of siliconconstituting each semiconductor micro-needle 2 to thermal oxidation.Since the above transparent electrode 4 is in contact with the top endof each semiconductor micro-needle 2, it is electrically connected toeach semiconductor micro-needle 2. Therefore, if a specified voltage isapplied between the transparent electrode 4 and the silicon substrate 1connected to the base ends of the semiconductor micro-needles 2 or ifthe quantized region Rqa is irradiated with light, light emission iscaused in each of the semiconductor micro-needles 2 by the quantum sizeeffects, thereby generating electroluminescence and photoluminescence.

Next, a description will be given to a method of manufacturing theoptical semiconductor apparatus. FIGS. 2(a) to 2(e) are cross-sectionalviews showing the transition of the structure of the opticalsemiconductor apparatus during its manufacturing process.

First, as shown in FIG. 2(a), a top insulating film 5 composed of asilicon dioxide film, a silicon nitride film, or the like is formed onthe silicon substrate 1 by thermal oxidation, CVD, or a like method.Thereafter, hemispherical grains 6 made of silicon are deposited thereonby LPCVD. In this case, if a He-based 20% SiH₄ gas is used as a rawmaterial and a flow rate is set to 300 ccm, the hemispherical grainswith a radius of several nanometers as shown in the drawing can beobtained.

In producing the hemispherical grains 6, it is also possible to use aSiH₄ gas in an atmosphere of hydrogen gas. In this case, it becomesparticularly easy to control the deposition of the hemispherical grains6.

Next, as shown in FIG. 2(b), the top insulating film 5 composed of asilicon dioxide film or a silicon nitride film is etched, using a firstdotted mask Msl consisting of the large number of hemispherical grains6, so as to form a second dotted mask Ms2 composed of the remainingportions of the top insulating film 5, which has been patterned intostripes corresponding to the pattern of the large number ofhemispherical grains 6. The etching of the top insulating film 5 on thesilicon substrate 1 is conducted, e.g., in an atmosphere of mixed gasesof CF4/CHF3=30/40 sccm under a pressure of 1 Pa with an RF power of 400W. After that, each hemispherical grain 6 is etched away.

Next, as shown in FIG. 2(c), the silicon substrate 1 is etched to aspecified depth, using the second dotted mask Ms2 patterned in stripes,so as to form a large number of semi-conductor micro-needles 2perpendicular to the surface of the silicon substrate 1. The etching isconducted in an atmosphere of mixed gases of C12/02=90/3 sccm under apressure of 1 Pa with an RF power of 200 W. The side portions of eachsemiconductor micro-needle 2 are substantially vertical to the surfaceof the silicon substrate 1 and stand substantially upright. As will bedescribed later, if the hemispherical grains 6 are formed underappropriate conditions, the semiconductor micro-needles 2 can be formedindependently of each other with no linkage.

Then, as shown in FIG. 2(d), the side portions of the semiconductormicro-needles 2 are covered with an insulating layer 3 composed of asilicon dioxide film so as to fill up the space surrounding eachsemiconductor micro-needle 2, followed by the flattening of the top endsthereof.

Furthermore, as shown in FIG. 2(e), the flattened portion of theinsulating layer 3 which covers the top ends of the semiconductormicro-needles 2 is removed so as to form the transparent electrode 4thereon.

In the above first embodiment, the top insulating film 5 and the firstdotted mask Ms1 are successively formed on the silicon substrate 1 andthen the second dotted mask Ms2 is formed from the top insulating film5, so that the silicon substrate 1 is etched using the second dottedmask Ms2. However, it is also possible to form the semiconductormicro-needles 2 by forming the first dotted mask Msl directly on thesilicon substrate 1 and then etching the silicon substrate 1, using thefirst dotted mask Ms1.

Next, a description will be given to the operation of the opticalsemiconductor apparatus thus constituted. Here, the region in which thesemiconductor micro-needles 2 are formed from the surface to a specifieddepth of the p-type silicon substrate 1 serves as the quantized regionRqa. When a voltage of 20 V is applied in the forward direction to thetransparent electrode 4 electrically connected to the semiconductormicro-needles 2, while setting the silicon substrate 1 to the groundpotential, visible electroluminescence is observed at room temperature.In the case of using silicon, since the electrons excited by theapplication of a voltage or the like generally undergo indirecttransitions, most of the energy resulting from the transition isconverted into heat, so that light emission in the visible region hasbeen considered difficult. However, since the quantized region Rqacomposed of silicon is constituted by the aggregate of semiconductormicro-needles 2 each having a radius of several nm in the above firstembodiment, the band width of silicon is expanded from 1.2 eV to 2.5 eVdue to the quantum size effects, while the excited electrons undergodirect transitions, thereby causing the emission of visible light due tothe direct transitions between the bands. Moreover, compared with theconventional porous silicon formed by anodization, the aggregate ofsilicon micro-needles 2 as used in the above first embodiment provides ahigh light emission intensity and a sharp emission spectrum.

Below, the reason for the advantages of the quantized region in thepresent embodiment over the conventional one will be deduced from adifference in structure therebetween. FIG. 4(a) shows the transversesectional structure of the grains used in the above manufacturingprocess in the case where they are made of amorphous silicon. FIG. 4(b)shows the transverse sectional structure of the grains used in the abovemanufacturing process in the case where they are made of <311>-orientedsingle- crystal silicon. Different conditions under which thesestructures are formed will be described later. FIG. 4(c) shows thetransverse sectional structure of the conventional porous silicon formedby anodization. As shown in FIG. 4(c), since the conventional poroussilicon is formed by anodization which renders silicon porous byprimarily using micro-pores in the dioxide film resulting from the anodeoxidation of silicon, a silicon wall is formed in the porous silicon.The thickness of the silicon wall, i.e., the distance d between twoadjacent micro-pores on both sides of the silicon wall varies greatlyfrom one portion to another (see distances d1 and d2 in the drawing). Itmay be considered that, if the distance d between two adjacentmicro-pores on both sides is excessively large (as with d2 in thedrawing), the quantum size effects cannot be caused. By contrast, sincethe semiconductor micro-needles 2 in the present invention formsubstantially discrete stripes in transverse section, as shown in FIGS.4(a) and 4(b), it can be considered that they have sufficiently smalldimensions to cause the quantum size effects, though their diameters maydiffer slightly depending on their directions. Consequently, a higherlight emission intensity and a sharper emission spectrum can beobtained.

FIG. 5 shows the characteristics of the current (injected current)flowing through the aggregate of semiconductor micro-needles 2 withrespect to the voltage applied to the transparent electrode 4. FIG. 6shows the light emission intensity of electroluminescence with respectto the injected current in the aggregate of semiconductor micro-needles2. It will be appreciated from FIGS. 5 and 6 that the light emissionintensity increases with an increase in the voltage applied to thetransparent electrode 4. FIG. 7 shows the characteristics of the lightemission intensity with respect to the voltage for carrier injection. Itwill be appreciated from FIG. 7 that color display elementscorresponding to light emission in individual colors such as red, blue,and yellow can be formed by varying the voltage for carrier injection.

As shown in FIGS. 2(a) to 2(e), the first embodiment has adopted, informing the quantized region Rqa composed of the aggregate ofsemiconductor micro-needles 2 of single-crystal silicon each having aradius of several nanometers, the same processing method as used in theprocess of manufacturing a normal semiconductor apparatus such as aMOSFET. That is, the space surrounding each semiconductor micro-needle 2is filled with the oxide film 3, so that the top ends thereof areflattened and that the transparent electrode 4 is electrically connectedto the quantized region. Therefore, the process used in the firstembodiment is interchangeable with the conventional process of producinga silicon wafer for manufacturing a normal semiconductor apparatus, sothat a conventional semiconductor apparatus such as a normal MOSFET canbe produced after producing the optical semiconductor apparatusaccording to the present invention.

Next, a detailed description will be given to the conditions in eachstep of the manufacturing process for the above optical semiconductorapparatus.

The method of forming the grains in the step shown in FIG. 2(a) has beenreported since 1990 to increase the capacity of a DRAM. For example,such a method is disclosed in: Ext. Abs. 22nd SSDM (1990) pp. 869-872 byY. Hayashide et al.; J. Appl. Phys. 71(1991) pp. 3538-3543 by H.Watanabe et al.; and Tech. Dig. of VLSI Symp (1991) pp. 6-7 by H. Itohet al. By adopting these methods, the grains can be formed easily.

FIG. 3 shows variations in the configuration of the grain when thedeposition temperature and the partial pressure of SiH₄ are varied at aconstant gas flow rate of 300 ccm. The graph inserted in the drawing isa map showing conditions under which silicon crystal phases are formed,which consists of: an amorphous region in which amorphous silicon isformed as grains; a <311>-oriented region in which single-crystalsilicon having the <311>-orientation perpendicular to the substratesurface is formed as grains; and a <110>-oriented region in whichsingle-crystal silicon having the <110> orientation perpendicular to thesubstrate surface is formed as grains.

In terms of the structure of the resulting grains, the following threeregions are important:

1. A HSG-aSi region in which hemispherical grains (HSG) and amorphoussilicon (aSi) are mixed;

2. A HSG region in which hemispherical grains are formed all over; and

3. A CTG region where several grains combine to form a cylindricaltrained grain (CTG) in the form of a crest when viewed from the surface.

The observation of the three regions has led to the following findings:

(1) The HSG region exists in the <311>-oriented region where grains wereformed at a temperature within a range of 570° C. to 580° C. under aSiH₄ partial pressure (formation pressure) within a range of 0.5 Torr to2.0 Torr;

(2) The HSG-aSi region exists in the vicinity of the boundary betweenthe amorphous region and the <311>-oriented region;

(3) The CTG region exists mainly in the vicinity of the boundary betweenthe <311>-oriented region and the <110>-oriented region;

(4) The HSG region exists in that area of the above <311>-orientedregion which is interposed between the above two regions (the HSG-aSiregion and the CTG region);

(5) As the grains become closer to amorphous silicon in terms ofstructure, the grains increase in size accordingly. As the grains becomecloser to the <110> orientation in terms of structure, on the otherhand, the grains decrease in size accordingly;

(6) The amorphous region expands increasingly as the partial pressure ofSiH₄ (formation pressure) increases;

(7) Different grain sizes result from different densities of nuclei forthe growth of the grains (metal such as Ni or W) on the film surface;and

(8) Consequently, if grains are deposited at a deposition temperature of560° C. to 590° C. with a SiH₄ partial pressure of 0.1 to 0.4 Torr,grains in the form of hemispheres and grains in the form of crests areobtained at a surface density of 0.4 to 0.7.

In the above embodiment, the side portions of the semiconductormicro-needles 2 made of single-crystal silicon are subjected to thermaloxidation so as to fill up the space surrounding each semiconductormicro-needle 2 with the insulating layer 3 composed of a silicon dioxidefilm. However, the present invention is not limited to the aboveembodiment. Even when the insulating layer is not provided, lightemission due to the quantum size effects is generated. However, if theside portions of each semiconductor micro-needle 2 is covered with theinsulating layer 3 formed by thermal oxidation, the following advantagescan be obtained. That is, not only impurities and foreign substances,which have been generated from the etching of the silicon substrate 1 inthe formation of the semiconductor micro-needles 2 and attached to theside portions thereof, can be locked in the insulating layer 3, but alsothese impurities and foreign substances can be prevented ever after fromentering into the quantized region Rqa composed of the aggregate ofsemiconductor micro-needles 2 of single-crystal silicon. Since thequantized region Rqa is protected from the intrusion of these impuritiesand foreign substances, influences of the atoms and molecules attachedto the side portions of the semiconductor micro-needles 2 can beeliminated, so that a uniform wavelength can be constantly reproduced asrequired, thereby providing a semiconductor apparatus, such as a siliconlight-receiving/light-emitting element, with a long lifespan.

The insulating layer 3 made of silicon dioxide or silicon nitride doesnot necessarily fill up the space surrounding each semiconductormicro-needle 2, either, as in the first embodiment. Even when theinsulating layer 3 is formed only in the vicinity of the surfaces ofsemiconductor micro-needles 2, the functions of locking impurities andpreventing their intrusion can be implemented. However, if the spacesurrounding each semiconductor micro-needle 2 is filled with theinsulating layer 3 as in the first embodiment, a short circuit betweenthe semiconductor micro-needles 2 can surely be prevented as well as thetop ends of the semiconductor micro-needles 2 can be flattened withoutimpairing the configuration thereof. Consequently, an electricalconnection can surely be provided between the semiconductormicro-needles 2 and the transparent electrode 4.

(Second Embodiment)

Next, a description will be given to a second embodiment. FIGS. 8(a) to8(e) illustrate the process of manufacturing the optical semiconductorapparatus according to the second embodiment. The manufacturing processused in the second embodiment is substantially the same as themanufacturing process used in the above first embodiment, except thatthe conditions under which the hemispherical grains 6 are deposited byLPCVD are changed and that the space surrounding each semiconductormicro-needle 2 is filled up with a silicon dioxide film 3 b formed byCVD or the like after the side portions of the semiconductormicro-needles 2 were covered with a thermal oxidation film 3 a, followedby the flattening of their surface regions. In other words, these twotypes of oxide films 3 a and 3 b constitute an insulating layer 3.

In the step of depositing the hemispherical grains 6, a He-based 15%SiH₄ gas is used as a raw material so as to deposit the hemisphericalgrains 6 under the conditions of gas flow rate of 100 ccm, depositiontemperature of 500° C. to 700° C., and SiH₄ partial pressure of 0.1 to0.4 Torr. If the gas flow rate and the deposition rate are set lower,the deposition can be accomplished at a lower deposition temperature.FIG. 9 shows variations in the configuration of the hemispherical grain6 when the deposition temperature and the SiH₄ partial pressure arevaried at a constant gas flow rate of 100 ccm. The map showing theconditions of FIG. 3 can be divided into the three regions of: (1)HSG-aSi region; (2) HSG region; and (3) CTG region depending on theconfiguration of the resulting grain, similarly to the first embodiment.

The observation of the three regions has led to the following findings:

(1) The HSG region can be obtained at a temperature of 500° C. to 650°C. under a SiH₄ partial pressure of 0.1 Torr to 0.4 Torr.

In addition to this, the same tendencies as described in (2) to (7) ofthe above first embodiment can be recognized.

(8) From the foregoing, it can be concluded that the properhemispherical grains 6 can be obtained in a wider range of depositiontemperature than in the above first embodiment.

Hence, in the present second embodiment, the range of the appropriatedeposition temperature can be expanded by changing the ratio of SiH₄ tothe He base in the raw material gas and by changing the gas flow rate.The space surrounding each semiconductor micro-needle 2 can moresatisfactorily be filled with the oxide film 3 b or nitride film formedby CVD than only with the thermal oxidation film as in the firstembodiment.

Although the thermal oxidation film 3 a is formed prior to the formationof the silicon dioxide film 3 b in the above second embodiment, thepresent invention is not limited to the above embodiment. It is alsopossible to form the whole insulating film 3 b by CVD for theconvenience of the process.

In this case, if the whole insulating layer 3 is composed only ofsilicon dioxide, light emission in a lateral direction can be obtained,since the refractive index of silicon dioxide is small. If the wholeinsulating layer 3 is composed only of silicon nitride, on the otherhand, a difference in coefficient of thermal expansion between siliconnitride and silicon imparts a compressive strain to the semiconductormicro-needles 2, so that the quantum size effects can be exerted moreremarkably. The same effects can be achieved by forming a siliconnitride film in place of the silicon dioxide film 3 b formed by CVD inthe present embodiment.

(Third Embodiment)

Next, a description will be given to a third embodiment for improvingthe configuration of the hemispherical grain 6. After the hemisphericalgrains 6 are formed by substantially the same manufacturing process asthat of the above first embodiment, the SiH₄ gas in a tube is evacuated,followed by annealing while introducing N₂ gas, which is an inactivegas, into the tube. FIG. 11 shows the relationship between the annealingperiod and the grain diameter and density. It will be appreciated thatthe grain diameter decreases with an increase in annealing period. Sincethe surface and interface tend to shrink with a decrease in graindiameter, the configuration of the grain becomes closer to a hemisphere,resulting in a high increase rate of the surface area of the grain. Ifthe annealing period becomes 2 minutes or longer, the region with nohemispherical grain expands. The increasing difficulty with which thehemispherical grains 6 are formed can be attributed to the increasingdegree of surface oxidization due to annealing, which interferes withthe growth of grains on the surface. Furthermore, two-step annealing canbe performed under two sets of conditions with different partialpressures of oxygen, thereby making the grain diameter of thehemispherical grains 6 more uniform.

FIGS. 10(a) to 10(c) are SEM photographs of hemispherical grains takenwhen common film-forming conditions (a temperature of 575° C., apressure of 1.0 Torr, and a 20% SiH₄ gas flow rate of 300 sccm) and thesame annealing temperature (575° C.) are adopted, while the otherannealing conditions are varied. FIG. 10(a) shows hemispherical grainsobtained when annealing was conducted in an atmosphere of N₂ under apressure of 1.0 Torr for 30 minutes immediately after the filmformation. FIG. 10(b) shows hemispherical grains obtained when annealingwas conducted in vacuum (about 0.01 Torr) for 2 minutes after the filmformation and then continued under a pressure of 0.14 Torr for 10minutes. FIG. 10(c) shows hemispherical grains obtained when annealingwas conducted in vacuum (about 0.01 Torr) for 5 minutes after the filmformation and then continued in an atmosphere of N₂ under a pressure of1.0 Torr for 30 minutes.

After the formation of the hemispherical grains 6, semiconductormicro-needles 2, the insulating layer 3, the transparent electrode 4 andthe like are formed in substantially the same process as used in theabove first embodiment.

Since the present third embodiment has reduced the diameter of thehemispherical grain 6 by annealing and has improved the configurationthereof so that it becomes closer to a hemisphere, semiconductormicro-needles 2 with a substantially uniform radius can be formed in aplane in the vicinity of the surface of the silicon substrate 1.Moreover, since the radius of semiconductor micro-needles 2 constitutingthe quantized region becomes uniform, the emission spectrum becomessharper, while the light emission intensity increases.

(Fourth Embodiment)

Next, a description will be given to a fourth embodiment. FIGS. 12(a)and 12(b) are cross sectional views for illustrating the procedure offorming the hemispherical grains in the fourth embodiment.

First, as shown in FIG. 12(a), crystal growth nuclei 8 serving as nucleifor the crystal growth of grains are formed on the top insulating film 5on the silicon substrate 1. The crystal growth nuclei 8 are made ofmetal such as Tin or rhodium. To form the nuclei, the silicon substrate1 with the top insulating film 5 deposited thereon is immersed in asurface treatment solution at ordinary temperature for 1 minute,followed by washing and drying. As the surface treatment solution, asolution for use in plating is used.

Next, as shown in FIG. 12(b), using these crystal growth nuclei 8, thehemispherical grains 6 of silicon are grown on the top insulating film 5by LPCVD. As a raw material, a He-based 15% SiH₄ gas is used at a gasflow rate of 100 ccm. The deposition is conducted at a depositiontemperature of 500 to 700° C. under a SiH₄ partial pressure of 0.1 to0.4 Torr. Under these conditions, the silicon grains 6 are selectivelydeposited over the crystal growth nuclei 8 so as to form the firstdotted mask Ms1 consisting of a large number of silicon granularmaterials 6.

Then, in accordance with the same process as that of the firstembodiment (see FIGS. 2(c) to 2(e)), the hemispherical grains,insulating layer, transparent electrode and the like are formed.

FIG. 13 is a view showing for comparison the distribution and diameterof the grains when the surface treatment, as shown in FIG. 12(a), wasperformed and the distribution and diameter of the grains when thesurface treatment was not performed. Without the surface treatment, themean value of the grain diameter is 110 □ and the maximum grain diameteris more than 200 □. With the surface treatment, on the other hand, themean value of the grain diameter is 60 □ and the maximum grain diameteris 120 □ or less. Thus, with the surface treatment for forming thecrystal growth nuclei 8 prior to the formation of the grains, thedistribution and size of the hemispherical grains 6 become uniform,resulting in a uniform distribution of the grains in a plane. Since theradius and distribution of the semiconductor micro-needles 2constituting the quantized region become uniform accordingly, theemission spectrum becomes much sharper, while the light emissionintensity increases uniformly in the plane.

In the silicon light receiving element thus constituted, a negativevoltage is applied to the p-type silicon substrate 1 so as to set thetop end of each semiconductor micro-needle at the ground potential,followed by the irradiation of the aggregate of semiconductormicro-needles (quantized region) with light from a high-pressure mercurylamp as a light source. As a result of the irradiation with light, theresistance value of the quantized region containing the semiconductormicro-needles is changed, so that the apparatus can be used as a lightreceiving element.

(Fifth Embodiment)

Next, a description will be given to a fifth embodiment. FIG. 14 is across sectional view of the optical semiconductor apparatus according tothe fifth embodiment. The basic structure of the optical semiconductorapparatus shown in FIG. 14 is substantially the same as that of thefirst embodiment shown in FIG. 1, except that the quantized region Rqaon the silicon substrate 1 is laterally isolated from other regions by adiscrete insulating layer 9. The depth of the discrete insulating layer9 is larger than the depth h of the semiconductor micro-needle 2. Inaddition, apart from the transparent electrode 4 over the semiconductormicro-needles 2, a lateral electrode 10 is formed so as to penetrate thediscrete insulating layer 9. The lateral electrode 10 is connected tothe silicon substrate 1 functioning as a lower electrode with respect tothe transparent electrode 4 functioning as an upper electrode of thesemiconductor micro-needles 2.

A description will be given to the operation of the opticalsemiconductor apparatus thus constituted. If a voltage (e.g., about 50Volt) is applied between the transparent electrode 4 and the lateralelectrode 10, a potential difference is generated between the top endand base end of each semiconductor micro-needle 2 in the quantizedregion Rqa, so that visible electroluminescence is caused at roomtemperature by the same quantum size effects as those obtained in thefirst embodiment. In the present fifth embodiment, the voltage forcarrier injection is varied from 25 to 200 Volt so that visibleelectroluminescence corresponding to individual light emission in red,blue, and yellow is observed. With the provision of the lateralelectrode 10 as in the present fifth embodiment, it becomes particularlyeasy to transmit signals between the quantized region Rqa of the opticalsemiconductor apparatus and the outside.

(Sixth Embodiment)

Next, a description will be given to a sixth embodiment. FIG. 15 is across sectional view of the optical semiconductor apparatus according tothe sixth embodiment. The basic structure of the optical semiconductorapparatus shown in FIG. 15 is substantially the same as that of theabove fifth embodiment shown in FIG. 14, except that the sixthembodiment uses the n-type silicon substrate 1 in which a p-well 11 ispartially formed and that the region extending from above the p-well 11to the surface of the silicon substrate 1 is doped with an n-typeimpurity. Each semiconductor micro-needle 2 in the quantized region Rqais formed by etching the silicon substrate 1 from the surface thereof toa depth reaching the inside of the p-well 11. In other words, the heighth of the semiconductor micro-needle 2 is larger than the depth of thep-n junction between the p-well 11 and its overlying portion of thesilicon substrate 1. Consequently, the lower portion of thesemiconductor micro-needle 2 closer to its base end is composed ofp-type silicon, while the upper portion of the semiconductormicro-needle 2 is composed of n-type silicon, thereby forming a p-njunction 2 a at a midpoint in the semiconductor micro-needle 2. Sinceanother p-n junction is also formed between the p-well 11 and the mainbody of the silicon substrate 1, the quantized region Rqa is isolatedfrom the n-type silicon substrate 1. The lateral electrode 10 isconstituted so as to be connected to the p-well 11.

When a voltage of 50 Volt is applied in the forward direction betweenthe transparent electrode 4 and the lateral electrode 10, the generationof visible electroluminescence at room temperature is also recognized inthe present sixth embodiment. By varying the voltage for carrierinjection from 25 to 200 Volt, the generation of visibleelectroluminescence corresponding to individual light emission in red,blue, and yellow is also recognized.

Thus, the above sixth embodiment provides the following effects inaddition to the same effects as obtained in the above fifth embodiment.That is, since the quantized region Rqa composed of the aggregate ofsemiconductor micro-needles 2 is isolated from other regions by thelateral discrete insulating layer 9 as well as from the n-type siliconsubstrate 1 by the p-well 11, even in the case where a large number ofquantized regions are formed on the silicon substrate, light emissioncan be generated individually in each of the quantized regions.Moreover, since the p-n junction is formed in each semiconductormicro-needle 2, carriers can be efficiently injected into eachsemiconductor micro-needle 2, thereby providing an optical semiconductorapparatus with excellent emission efficiency.

(Seventh Embodiment)

Next, a description will be given to a seventh embodiment. FIG. 16 is across sectional view of the optical semiconductor apparatus according tothe seventh embodiment. The basic structure of the optical semiconductorapparatus of the present seventh embodiment is substantially the same asthat of the above fifth embodiment shown in FIG. 14. Accordingly, thequantized region Rqa composed of the aggregate of semiconductormicro-needles 2 is formed on the p-type silicon substrate 1 and thereare further formed the transparent electrode 4 over the quantized regionRqa, the discrete insulating layer 9 surrounding the quantized regionRqa, and the lateral electrode 10 connected to the silicon substrate 1through the discrete insulating layer 9. In the present embodiment,however, the quantized region Rqa composed of the aggregate ofsemiconductor micro-needles 2 is not constituted by a single-layerstructure, but by a structure in which linearly-striped quantizedregions 12 a, each containing both semiconductor micro-needles 2 and theinsulating layer 3 for filling up the space surrounding eachsemiconductor micro-needle 2, and linearly-striped discrete layers 13 a,each composed of a silicon dioxide film, are alternately arranged. FIG.17(a) is a schematic plan view of the linearly striped structures, inwhich the linearly-striped quantized regions 12 a (dotted portions inthe drawing) and the linearly-striped discrete layers 13 a (hollowportions in the drawing) are alternately arranged at such intervals asto constitute a one-dimensional Fresnel lens.

FIG. 17(b) is a plan view showing another example of the linearlystriped structures, in which ring-shaped quantized regions 12 b andring-shaped discrete layers 13 b are alternately arranged so as toconstitute a two-dimensional Fresnel lens.

If a voltage is applied in the forward direction between the transparentelectrode 4 and lateral electrode 10, the generation of visibleelectroluminescence at room temperature is also recognized in thepresent embodiment.

In the optical semiconductor apparatus thus constituted, since theregions 12 a or 12 b and the discrete layers 13 a or 13 b arealternately arranged, the whole quantized region Rqa functions as aFresnel lens. Consequently, an additional light condensing apparatus isnot necessary. That is, if light emission is generated in the quantizedregion Rqa constituting the one-dimensional Fresnel lens shown in FIG.17(a) or the two-dimensional Fresnel lens shown in FIG. 17(b), lightadvancing in a direction perpendicular to the surface of the siliconsubstrate 1 is condensed onto a line or point, thereby condensing lightinto an intended region. Therefore, if an additional light receivingelement is placed in the vicinity of the focus, the light emitted fromthe optical semiconductor apparatus is efficiently condensed into thelight receiving element, so that it becomes possible to transmitelectric power converted into signals or light to a distant location viathe light receiving element. In the case of using the quantized regionas a wavelength converting element or light receiving element, itbecomes possible to irradiate the entire quantized region Rqa with lightfrom a linear optical source or dotted optical source.

(Eighth Embodiment)

Next, a description will be given to an eight embodiment. FIG. 18 showsthe cross sectional structure of the optical semiconductor apparatusaccording to the eighth embodiment, which is basically the same as thestructure of the optical semiconductor apparatus according to the aboveseventh embodiment shown in FIG. 15. That is, there are disposed: thequantized region Rqa composed of the aggregate of silicon semiconductormicro-needles 2 each having the p-n junction 2 a and of the insulatinglayer 3; the transparent electrode 4 over the quantized region Rqa; thep-well 11 holding the base end of each semiconductor micro-needles 2 inthe quantized region Rqa and being electrically insulated from then-type silicon substrate 1; the discrete insulating layer 9 surroundingthe quantized region Rqa; and the lateral electrode 10 connected to thep-well 11 through the dielectric insulating layer 9.

In the process of forming the above quantized region Rqa of the presentembodiment, the p-well 11 is formed in the silicon substrate 1 and thenthe overlying region is turned into an n region, followed by the etchingof the silicon substrate 1 till the p-well 11 is reached, using thefirst or second dotted mask as used in the above first embodiment. Inaccordance with the formation process, the p-n junction 2 a is formed ineach semiconductor micro-needle 2.

In the present eighth embodiment, two lateral electrodes 10 are disposedon both sides of the quantized region Rqa and a radio-frequency powersource 14 for applying a radio-frequency voltage to a circuit 17connecting these two lateral electrodes 10. To the circuit 18 connectingthe circuit 17 and the transparent electrode 4 are connected in series aswitch 15 for opening and closing the circuit 18 and a DC power source16.

A description will be given to the operation of the silicon lightemitting element thus constructed.

As shown in FIG. 19, when a radio-frequency electric power is applied tothe silicon crystal, electrons in a crystal lattice of silicon(indicated by solid circles) are excited by an electric field varyingwith high frequencies so as to move periodically to a certain extent. Inthe present embodiment, since the radio-frequency power source 14 isconnected to the two lateral electrodes 10 formed in the dielectricinsulating layer 9 in the vicinity of the semiconductor micro-needles 2,the electrons excited by the radio-frequency electric power areaccumulated in the p-type silicon substrate 1. The accumulated electronsare introduced into each semiconductor micro-needle 2 in the quantizedregion Rqa by the voltage applied in the forward direction via thetransparent electrode 4, so that a large amount of electrons areinjected through the p-n junction 2 a in each semiconductor micro-needle2. The injection increases the light emission intensity in the quantizedregion Rqa. To the transparent electrode 4 is applied a voltage of 100Volt. In this case also, visible electroluminescence is observed at roomtemperature.

As described above, in the present eighth embodiment, the electronsexcited by the application of radio-frequency electric power to thep-type silicon substrate 1 are introduced into each semiconductormicro-needle 2 in the quantized region Rqa, so that a large amount ofelectrons are injected through the p-n junction 2 a. As a result,intense light emission is caused efficiently in the quantized region Rqaeven by a weak signal supplied to the transparent electrode 4.

Although the two lateral electrodes 10 are formed on both sides of thequantized region Rqa in the above eighth embodiment, three or morelateral electrodes 10 surrounding the quantized region Rqa may be formedso as to generate a rotating magnetic field in the quantized region Rqaby applying to the lateral electrodes radio-frequency electric powerhaving the same frequency with its phase varying in increasing ordecreasing order. In this case, higher emission efficiency can beobtained.

(Ninth Embodiment)

Next, a description will be given to a ninth embodiment. FIG. 20partially shows the cross sectional structure of an opticalsemiconductor apparatus according to the ninth embodiment. In thepresent embodiment, the quantized region Rqa composed of the aggregateof semiconductor micro-needles 2 and a photodiode consisting of a p-typeregion 20 a and an n-type region 20 b are formed on the siliconsubstrate 1. Over the photodiode 20 and quantized region Rqa is providedthe transparent electrode 4 to be used in common. In addition, a drivingcircuit 21 is provided for applying a specified voltage between theabove transparent electrode 4 and the silicon substrate 1. That is, ifan optical signal Sgo0 is input to the photodiode 20 with a constantbias being applied to the photodiode 20 via the driving circuit 21, anelectromotive force is generated in the photodiode 20 so that anelectromotive force generated in the photodiode 20 is converted by thedriving circuit 21 to a voltage of, e.g., 15 V, which is then applied toeach semiconductor micro-needle 2 in the quantized region Rqa. As aresult, each semiconductor micro-needle 2 emits light which is output asa second optical signal Sgo2. In this case, the emission wavelength canbe changed by changing the manufacturing specification of eachsemiconductor micro-needle 2.

Next, the process of manufacturing the optical semiconductor apparatuswith a structure obtained by slightly modifying the structure shown inFIG. 20 will be described with reference to FIGS. 21(a) to 21(c). First,as shown in FIG. 21(a), the quantized region Rqa composed of theaggregate of semiconductor micro-needles 2 is formed in a given portionof the silicon substrate 1 made of silicon. Next, as shown in FIG.21(b), an n region 24 a is formed deep by injecting As⁺ ions into thesilicon substrate 1 by using the photo resist mask with an openingformed in a region different from the above quantized region Rqa,followed by the shallow formation of an n region 24 b by injecting B⁺ions into the silicon substrate 1. In this step, the intermediate regionin which either As ions or B⁺ ions are hardly injected becomes anintrinsic region 24 c, thereby forming the photodiode 24 of so-calledPIN structure which consists of the p region 24 a, n region 24 b, andintrinsic region 24 c. The photodiode 24 may also be formed bypreliminarily trenching deep that portion of the silicon substrate inwhich the photodiode 24 is to be formed and then epitaxially growing theregions 24 a, 24 c, and 24 b in this order. Subsequently, as shown inFIG. 21(c), a conductive wire 25 which transmits light (made of, e.g.,Au) is formed on the silicon substrate 1 and then the driving circuit 21is further formed.

The optical semiconductor apparatus shown in FIG. 21(c) can beconstituted so that the photodiode 24 receives the optical signal Sgo0at a certain wavelength, while the second optical signal Sgo2 is outputfrom each semiconductor micro-needle 2 in the quantized region Rqa. Thewavelength of the second optical signal Sgo2 can be changed by changingthe structure or manufacturing process. Since such an opticalsemiconductor apparatus can be manufactured by a process for a silicondevice, it can be accommodated in a microchip, which makes it applicableto optical communication and the like.

It is also possible to produce a device with the function of modulating,with light, information being transmitted over a signal path by adding acircuit for converting the second optical signal Sgo2 to an electricsignal to the structure of the optical semiconductor apparatus accordingto the above embodiment.

(Tenth Embodiment)

Next, a description will be given to a tenth embodiment, in which astress sensor is constituted using an aggregate of semiconductormicro-needles. FIG. 22(a) shows the structure and principle of operationof the stress sensor in the tenth embodiment. That is, in the presentembodiment, the quantized region Rqa composed of the aggregate ofsemiconductor micro-needles 2 and the transparent electrode 4 are formedon the silicon substrate 1, as shown in the drawing. In the opticalsemiconductor apparatus is also disposed the driving circuit 28 forapplying a voltage to the quantized region Rqa via the transparentelectrode 4.

In FIGS. 22(a)-(d) show three variations in the configuration of eachsemiconductor micro-needle 2 in response to a change in the stressexerted thereon. FIG. 22(b) shows the semiconductor micro-needle 2 withno stress exerted thereon. FIG. 22(c) shows the semiconductormicro-needle 2 with a compressive force exerted thereon towards the longwavelengths. FIG. 22 (d) shows the semiconductor micro-needle 2 with atensile stress exerted towards the short wavelengths. As describedabove, when a voltage is applied to both ends of each semiconductormicro-needle 2, a bandgap widening occurs in the semiconductormicro-needle 2 due to the quantum size effect, so thatelectroluminescence in the visible region is observed. It is well knownthat the amount of the bandgap widening ΔE is inversely proportional tothe diameter of each semiconductor micro-needle 2. Therefore, if thediameter d of each semiconductor micro-needle 2 on the order of 10 nm ischanged by a force exerted from outside, the emission wavelength λ whichis inversely proportional to 1/ΔE is also changed. For example, if acompressive stress is exerted on the semiconductor micro-needle 2, asshown in FIG. 22, the diameter d of the semiconductor micro-needle 2increases in accordance with the Poisson's ratio, while the emissionwavelength λ shifts toward longer wavelengths. On the other hand, if atensile stress is exerted on the semiconductor micro-needle 2, as shownin FIG. 22, the diameter d of the semiconductor micro-needle 2 decreasesin accordance with the Poisson's ratio, while the emission wavelengthshifts toward shorter wavelengths.

FIG. 23(a) shows an example of the structure of a stress sensor using anaggregate of semiconductor micro-needles. In addition to the basicstructure shown in FIG. 22(a), transparent probes 29 a and 29 b fortransmitting an external force to each semiconductor micro-needle 2 inthe quantized region Rqa are provided on the top and bottom faces of thesilicon substrate 1. FIG. 23(b) shows the emission spectra of the secondoptical signal Sgo2 output from the quantized region Rqa, in which thecenter emission wavelength of 630 nm has shifted about 10 nm towardshorter wavelengths and toward longer wavelengths in response tocompression and stretching under 1 Pa, respectively. In particular, byconnecting the probes 29 a and 29 b for detecting a stress to an objectfrom which an external force is to be detected so as to use the probes29 a and 29 b and the transparent electrode 4 as stress transmittingmeans, a stress can be converted into an optical signal with highsensitivity. In the present embodiment also, the optical semiconductorapparatus can be manufactured easily by means of the process for asilicon device.

As will be described in the following embodiment, it is also possible inthe present embodiment to detect the second optical signal Sgo2 from thequantized region Rqa by means of a light receiving element and toconvert it into an electric signal.

(Eleventh Embodiment)

Next, a description will be given to an eleventh embodiment. FIG. 24shows the overall structure of the semiconductor apparatus according tothe eleventh embodiment, which can be used as a pocket computer withhigh performance. There are provided on a semiconductor chip 50: acentral processing circuit 51 for processing signals associated witheach circuit on the semiconductor chip 50; a memory 52; an electric I/Ocircuit 53; a light receiving unit 54 for receiving an optical signalvia a condensing mechanism; a first light-emitting unit for outputtingan optical signal; a second light-emitting unit 56 for displaying asignal via pixels on the semiconductor chip 50; a sound-wave sensor unit57 and sound-wave output unit 58 for inputting and outputting a soundwave; a display-panel driving circuit 59 for driving a display panelcomposed of a TFT liquid-crystal panel; and a power-source supply unit60 for converting an optical signal from the outside into an electricsignal so that each circuit on the semiconductor chip 50 is suppliedwith the resulting electric signal as the power source. The above memory52, electric I/O circuit 53, light receiving unit 54, light emittingunits 55 and 56, sound-wave sensor unit 57, sound-wave output unit 58,and display-panel driving circuit 59 are connected to the centralprocessing circuit 51 via signal lines.

In this structure, of the units described above, such units as thecentral processing circuit 51, memory 52, electric I/O circuit 3 have aMOS transistor structure similar to that used in the conventionalsilicon integrated circuit. The light receiving unit 54 has a commonphototransistor structure.

On the other hand, each of the first light emitting unit 55 and secondlight emitting unit 56 is constituted by the quantized region composedof an aggregate of semiconductor micro-needles similar to that used inthe above first embodiment and the like.

FIGS. 25(a-1) to 25(d-2) show the process of forming an aggregate ofsemiconductor micro-needles in the present embodiment. In each of thedrawings, FIGS. 25(a-1), 25(b-1), 25(c-1) and 25(d-1) are showing thecross sectional views, while FIGS. 25(a-2), 25(b-2), 25(c-2), and25(d-2) are showing the plan views. First, as shown in FIGS. 25(a-1) and25(a-2), a photoresist film Frs is formed on the silicon substrate 1.Next, as shown in FIGS. 25(b-1) and 25(b-2), F2 vacuum ultraviolet laserlight, which has been divided into two beams, are obliquely madeincident so that the two beams overlap each other. Subsequently, theinterference fringe is exposed to be developed. After the firstexposure, those portions of the photoresist film Frs corresponding tothe intensely exposed portions of the interference fringe are removed,resulting in a striped mask pattern, as shown in the right-hand view ofFIG. 25(b-1). The silicon substrate 1 in the position shown in FIG.25(b-2) is then rotated 90 degrees, though the drawing thereof isomitted here, so that the same two beams of laser light are madeincident thereon, thereby eventually providing the first dotted mask Ms1which is several nm square. Since the interference fringe of the laserlight is formed with a specified pitch determined by the wavelength andincident angle, the size of the dotted mask Ms1 can be regulated asdesired. Next, as shown in FIG. 25(c-1) and 25(c-2), the siliconsubstrate 1 is etched to a depth of 0.5 to several μm using the firstdotted mask Ms1, thereby forming the aggregate of semiconductormicro-needles 2. The etching conditions are the same as those used inthe first embodiment. Then, after removing the photoresist film Frs, thespace surrounding each semiconductor micro-needle 2 is filled with theinsulating layer 3 by subjecting the side portions of each semiconductormicro-needle 2 to thermal oxidation, followed by surface flattening.Subsequently, as shown in FIGS. 25(d-1) and 25(d-2), the flattened oxidelayer on the top ends of the semiconductor micro-needles 2 is removed,followed by the formation of the transparent electrode 4 over thequantized region Rqa.

The formation of the dotted mask Ms1 by patterning the photoresist filmFrs is not limited to the formation of the interference fringe as in thepresent embodiment. It is also possible to form a large number oflongitudinal and transverse trenches in a pre-baked photoresist mask byhorizontally moving the silicon substrate with a probe needle of thecantilever of an atomic force microscope being pressed onto the siliconsubstrate under a specified pressure, so that the remaining dottedportions constitute the dotted mask. It is also possible, in forming thedotted mask by patterning the photoresist film, to form the oxide filmon the silicon substrate 1, as in the above first embodiment, and thenpattern the oxide film into dots by using the first dotted mask composedof the photoresist film, so that they serve as the second dotted mask inetching the semiconductor.

FIG. 26 is a plan view of the semiconductor chip 50 according to thepresent embodiment, in which the second light emitting unit 56 composedof a large number of quantized regions Rqa (aggregates of semiconductormicro-needles) arranged in matrix are disposed on the semiconductor chip50. That is, each of the quantized regions Rqa in the second lightemitting unit 56 is turned on or off in response to a signal so that aspecified pattern is displayed, thereby displaying, e.g., the results ofthe defective/nondefective judgments on the circuits on thesemiconductor chip 50.

On the other hand, the optical signal output from the first lightemitting unit 55 is transmitted to the outside via an optical fiber.FIG. 27 shows the cross sectional structure of the first light emittingunit 55, in which the transparent electrode 4 is formed over thequantized region Rqa composed of an aggregate of semiconductormicro-needles and a convex lens 61 serving as a light condensingmechanism is disposed on the transparent electrode 4 with a filterinterposed therebetween. The second optical signal Sgo2 condensed by theconvex lens 61 is output to the outside via the optical fiber (notshown). The filter 62 is a band-pass filter produced by stacking aplurality of transparent thin films, each having a different refractiveindex, so as to cause multiple interference. Although the provision ofthe filter 62 is not mandatory, if it is required to transmit the signalover a comparatively long distance, the filter can suppress theattenuation of a signal by reducing the width of the optical band, sothat the filter is preferably provided over the quantized region Rqa ofthe first light emitting unit 55. With the provision of the additionalcondensing mechanism such as a convex lens, the connection with theoptical fiber, which has been provided substantially perpendicular tothe surface of the semiconductor chip 50, is improved.

The display-panel driving circuit 59 is composed of a normal MOSintegrated circuit, which is for using a liquid-crystal displayapparatus (LCD) if a displaying function covering a large area isrequired.

In the sound-wave sensor unit 57, a thin diaphragm 63 supported at fourpoints is formed on the semiconductor chip 50, as shown in FIGS. 28(a)and 28(b), so that a sound wave is converted into an electric signalbased on a phenomenon that the amount of displacement of the diaphragm63 caused by the sound wave is proportional to a variation in theresistance of a bridge (a piezoresistance effect). A piezoresistanceeffect element has been developed as a stress sensor, the technique ofwhich is applied to the present embodiment. It is also possible todetect a variation in capacitance between the electrode and thesubstrate, as if with a condenser microphone.

The above sound-wave output unit 58, comprising a cantilever diaphragm64 as shown in FIG. 29, is constituted so that the diaphragm 64 isvibrated by an electrostatic force caused by a sound signal, therebygenerating a sound wave. It is also possible to drive an externallow-power speaker with a sound signal, instead of a unit having such astructure.

The above power-source supply unit 60 is a circuit for converting lightfrom the outside into electric energy, so that the resulting electricenergy is supplied to each circuit on the semiconductor chip 50. Thepower-source supply unit 60 consists of: a photodiode for receivinglight and converting it into a current signal; and a constant voltagecircuit for receiving the current signal and generating a constantvoltage of the order of 3 to 5 V (the drawing thereof is omitted). Whenthe power source is supplied using not light but an electromagnetic wavesuch as a millimeter wave or a microwave, a detection circuit andconstant voltage circuit, composed of an antenna and a diode, can beused instead.

As has been described in the present embodiment, a wireless operation ofthe semiconductor apparatus can be accomplished by inputting a signalwith the use of light or supplying electric power with the use of light.Moreover, the delay of a signal resulting from a parasitic impedance canbe minimized by not providing wires for receiving signals and electricpower. Since multiple functions can be implemented by one chip, thesemiconductor apparatus according to the present embodiment cancontribute greatly to the miniaturization of a portable computer and thelike. Since the semiconductor apparatus according to the presentembodiment is provided with the function of inputting and outputting asignal using a sound wave, it can contribute to the advancement of ahuman interface of computers. Also in the process of manufacturing thesemiconductor apparatus, a part of the wiring step is not required anymore, resulting in a reduction in manufacturing cost and a higherproduction yield. Furthermore, if an emission displaying function and aself-checking function are used in combination, only defective productscan easily be screened by the displaying function, so that checking costand time can be reduced.

(Twelfth Embodiment)

Next, a description will be given to a twelfth embodiment. FIGS. 30(a)to 30(d) show the process of manufacturing the optical semiconductorapparatus in which a light receiving element and a light emittingelement are incorporated into an integrated circuit. First, as shown inFIG. 30(a), there is formed on a p-type silicon substrate 1 a MOSFET 70consisting of: an n-type source 71; an n-type drain 72; a gate oxidefilm 73; a gate electrode 74; and an inter-layer insulating film 75.Next, as shown in FIG. 30(b), the quantized region Rqa composed of anaggregate of semiconductor micro-needles and functioning as a lightemitting element is formed in that region with an opening of theinter-layer insulating film 75 which is adjacent to the region in whichthe above MOSFET 70 is to be formed, in accordance with the process usedin the above first embodiment. Then, as shown in FIG. 30(c), aninsulating film 76 is formed with an opening corresponding to eachquantized region, followed by the formation of the transparent electrode4 composed of an ITO so as to cover the quantized region Rqa and a partof the above insulating film 76. Thereafter, a metal wire 77 forelectrically connecting the drain 72 to the transparent electrode 4 isformed. Then, as shown in FIG. 30(d), over the wire 77 made of metal,polysilicon, and the like and over the transparent electrode 4, aninter-substrate insulating film 78 is formed with an openingcorresponding to the quantized region Rqa, followed by surfaceflattening.

On the other hand, there is formed on another silicon substrate 1 b, aphotodiode 79 consisting of a p region and an n region and functioningas a light receiving element is formed instead of the quantized regionRqa formed in the steps shown in FIGS. 30(a) to 30(d), though thedrawing thereof is omitted. On the photodiode 79 is disposed thetransparent electrode 4, and the inter-substrate insulating film 78 withan opening corresponding to the photodiode is further formed.

FIG. 31 shows the cross sectional structure of the optical semiconductorapparatus in which the above two silicon substrates 1 a and 1 b arejoined with the inter-substrate insulating film 78 interposedtherebetween, so that the quantized region Rqa and the photodiode 79 areopposed to each other. The drain 72 of the MOSFET 70 serving as theoutput electrode of the lower logic circuit is connected to thequantized region Rqa composed of an aggregate of semiconductormicro-needles, each having a thickness of 0.1 μm, via the transparentelectrode 4. If the electric potential of the drain 72 as the outputelectrode is raised to 2 V, the first electric signal Sgel is output sothat an electric field of about 0.2 MV/cm is applied to eachsemiconductor micro-needle in the quantized region Rqa. Upon receivingthe first electric signal Sgel, each semiconductor micro-needle emitslight, so that the second optical signal Sgo2 is output from thequantized region Rqa. When the second optical signal Sgo2 transmitted bythe transparent electrode 4 is input to the photodiode 79, the thirdelectric signal Sge3 is output from the photodiode 79. The thirdelectric signal Sge3 is input to the drain of the lateral MOSFET 70 viathe metal wire 77. The subsequent signal processing is performed in thesame manner as in a normal integrated circuit.

Thus, the present embodiment provides an optical semiconductor apparatusinto which a composite device having an optical processing function isincorporated, wherein an output signal is converted from an electricsignal to an optical signal by a light receiving element formed in anintegrated circuit and then converted again to an electric signal.

(Thirteenth Embodiment)

Next, a description will be given to a thirteenth embodiment. FIGS.32(a) to 32(d) illustrate the process of manufacturing the opticalsemiconductor apparatus, which is constituted so that a light emittingelement and a light receiving element are opposed to each other with atrench interposed therebetween. First, as shown in FIG. 32(a), thequantized region Rqa, composed of an aggregate of semiconductormicro-needles and functioning as a light emitting element, and thephotodiode 79, consisting of a p region and an n region and functioningas a light receiving element, are formed in two adjoining regions of thesilicon substrate 1. Next, as shown in FIG. 32(b), the inter-layerinsulating film 75 and the wire 77 made of polysilicon are formed overthe quantized region Rqa and photodiode 79. In this case, it is notrequired to form a transparent electrode over the quantized region Rqaand photodiode 79. Next, as shown in FIG. 32(c), that region of thesilicon substrate 1 which is interposed between the quantized region Rqaand the photodiode 79 and which includes a part of the quantized regionRqa and a part of the photodiode 79 is etched so as to form a trench 80.

FIG. 32(d) shows the cross sectional structure of the opticalsemiconductor apparatus that has been finished. As shown in the drawing,one side portion of the quantized region Rqa serving as a light emittingelement and one side portion of the photodiode 79 serving as a lightreceiving element are exposed. In other words, the quantized region Rqaand the photodiode 79 are formed in the side walls of the trench 80 soas to face each other. As shown in FIG. 1 of the first embodiment, sincethe insulating layer 3 composed of a transparent silicon dioxide film isformed so as to surround each semiconductor micro-needle 2 in thequantized region Rqa, light emission from the quantized region Rqa isalso observable from its lateral side. Consequently, in the presentembodiment, if the first electric signal Sgel is input to the quantizedregion Rqa via the wire 77, the second optical signal Sgo2 is outputfrom the quantized region Rqa, which is further converted into the thirdelectric signal Sge3 by the photodiode 79. In the present embodiment,the joining of the two substrates is not particularly required and thesame function as performed by the three-dimensional integrated circuitstructure of the twelfth embodiment can be performed by atwo-dimensional integrated circuit. Moreover, since the presentembodiment is free from problems associated with alignment, a compositedevice having an optical processing function can easily be disposed inthe manufacturing process.

Although each of the above embodiments has used a single-crystal siliconsubstrate, the present invention is not limited to these embodiments.The present invention is also applicable to, e.g., single-elementsemiconductors such as germanium and to group II-V compoundsemiconductors such as GaAs, GaP, GaN, and InP. In particular, if thesemiconductor micro-needles are formed from a material having a bandstructure of direct-transition type such as Ga-As, light emissionintensity is advantageously increased due to the quantum size effects aswell as laser light with excellent characteristics can easily beobtained. Moreover, the semiconductor micro-needles should notnecessarily be formed from a single-crystal material. It is alsopossible to constitute a highly efficient solar battery or the likebased on a highly efficient photoelectric conversion, which can beperformed by using, e.g., an aggregate of amorphous siliconmicro-needles.

Although each of the above embodiments has formed the aggregate of thesemiconductor micro-needles 2 directly on the silicon substrate 1, thepresent invention is not limited to these embodiments. It is alsopossible to form an aggregate of semiconductor micro-needles on thesilicon substrate with an insulating film interposed therebetween. Inother words, a so-called SOI structure can be formed.

We claim:
 1. An aggregate of semiconductor micro-needles comprising: alarge number of semiconductor micro-needles juxtaposed in a substrate,each of said semiconductor micro-needles having a diameter sufficientlysmall to cause the quantum size effects, and an insulating layer formedon the side portions of each of said semiconductor micro-needles,wherein said insulating layer is incorporated into said aggregate ofsemiconductor micro-needles by filling up the space surrounding each ofthe semiconductor micro-needles to the top end thereof.
 2. An aggregateof semiconductor micro-needles according to claim 1, wherein each ofsaid semiconductor micro-needles is formed substantially perpendicularto the surface of said substrate.
 3. An aggregate of semiconductormicro-needles according to claim 1, wherein said semiconductormicro-needles are formed discretely.
 4. An aggregate of semiconductormicro-needles according to claim 1, wherein said insulating layer iscomposed of an oxide.
 5. An aggregate of semiconductor micro-needlesaccording to claim 1, wherein said insulating layer is composed of anitride.
 6. An aggregate of semiconductor micro-needles comprising: alarge number of semiconductor micro-needles juxtaposed in a substrate,each of said semiconductor micro-needles having a diameter sufficientlysmall to cause the quantum size effects, and an insulating layer formedon the side portions of each of said semiconductor micro-needles, saidinsulating layer incorporated into said aggregate of semiconductormicro-needles by filling up the space surrounding each of thesemiconductor micro-needles, wherein said semiconductor micro-needlesand said insulating layer are formed to have substantially the samedimension in the axial direction of the semiconductor micro-needles, andthe top ends of the semiconductor micro-needles and of the insulatinglayer are flattened.
 7. An aggregate of semiconductor micro-needlescomprising: a large number of semiconductor micro-needles juxtaposed ina substrate, each of said semiconductor micro-needles having a diametersufficiently small to cause the quantum size effects, and an insulatinglayer formed on the side portions of each of said semiconductormicro-needles, said insulating layer incorporated into said aggregate ofsemiconductor micro-needles by filling up the space surrounding each ofthe semiconductor micro-needles, wherein said insulating layer iscomposed of two layers of an inner oxide layer surrounding each of saidsemiconductor micro-needles and an outer nitride layer over the inneroxide layer.